The interaction of keratinocytes and epidermal nerve fibers has emerged as an important interface in sensory transduction and pain and may be a factor in the mechanisms underlying painful peripheral neuropathies. Keratinocytes express receptors and channels that enable them to "sense" mechanical and thermal stimuli and transmit signals to epidermal nerve fibers through the release of messenger molecules. Growth factors and cytokines secreted from keratinocytes are also likely to impact long-term changes within the sensory neurons that innervate epidermis. Conversely, neuropeptides contained within sensory neurons have the ability to modulate keratinocytes, including their production and secretion of cytokines and growth factors. Partial peripheral nerve injury that leads to neuropathic pain is associated with degeneration of injured nerve fibers and altered function of adjacent uninjured fibers. The impact of altered epidermal innervation on the dynamic neuro-keratinocyte relationship is unknown. The objective of this R21 proposal is to determine the effects of epidermal innervation on keratinocyte protein expression and function. Specific Aim 1 will address the hypothesis that nerve injury-induced changes in innervation will alter keratinocyte protein expression and function. Epidermal innervation and nerve injury- induced hypersensitivity will be correlated with keratinocyte expression of receptors and channels implicated in sensory transduction as well as cytokines known to sensitize sensory neurons. Functional changes in epidermis will be evaluated based on measurement of keratinocyte ATP release. Specific Aim 2 will determine the effects of sensory neurons on protein expression and function of keratinocytes in organotypic culture where neuronal input will be introduced by co-culture with sensory neurons. These experiments will address the hypothesis that selected subsets of sensory neurons will have differential effects on keratinocytes. Biochemical approaches will be used to identify candidate mediators of neuro-keratinocyte signaling. Changes in the dynamic neuro-keratinocyte relationship following nerve injury may contribute to neuropathic pain mechanisms through sensitization of surviving epidermal nerve fibers and changes in keratinocyte transduction of sensory stimuli. Therefore, neuro-keratinocyte interactions and their modulation by nerve injury represent a previously unexplored component of the pathobiological consequences of nerve injury, and their understanding may lead to identification of novel peripheral therapeutic targets for neuropathic pain. PUBLIC HEALTH RELEVANCE: The proposed project will analyze the interaction between two important structures in the transmission of sensory information: sensory nerves and the epidermis of the skin. These studies will identify a pattern of keratinocyte changes associated with nerve injury that will provide a foundation for in-depth analysis of the contribution of neuro-keratinocyte interactions to pain. Manipulation of these interactions may be able to provide a peripherally restricted therapeutic strategy.